The present invention relates to a coated ion exchange material suitable for use as a chromatography medium, and a method of forming and using this material.
In one form of liquid chromatography, columns are packed with a discrete organic polymer granule or particle medium having functionally active surfaces. Materials for performing liquid chromatography are known where only thin outer surfaces of the chromatographic support materials are available for active exchange of ions with liquid media. For example, Small, et al. U.S. Pat. No. 4,101,460 describes an ion exchange composition comprising an insoluble synthetic resin substrate having ion-exchanging sites on its available surface and a finely divided insoluble material microparticles) irreversibly attached to this substrate by electrostatic forces. An exemplified microparticle is formed from latex.
A disadvantage associated with the latex coating procedure is that it can take a substantial period of time, e.g., days or even weeks, to make an optimized packed column. Such procedures typically require applying the coating after the column is packed which increases the manufacturing time and labor compared to synthetic methods which can provide a finished product prior to packing. This is because the packing can be made more efficiently in large batches rather than on a column-by-column basis. Also, latex synthesis is generally limited to water insoluble monomers, significantly limiting the choice of available monomers.
Other particulate bed materials with ion exchange layering particles irreversibly bound to the outer surface of support particles are described in Barretto, U.S. Pat. No. 5,532,279. In one embodiment, Barretto describes forming a complex by contacting a suitable dispersant with monomer in an aqueous solution in which the monomer is insoluble. Under suitable conditions for suspension polymerization, the monomer will polymerize to form resin support particles having a dispersant irreversibly attached to those particles. Fine synthetic layering particles are bound to the support particles. A number of other embodiments are disclosed for irreversible attachment.
Another form of ion chromatographic medium is made by forming a coating by binding a solution of a preformed polymer with saturated carbon chain backbones including leaving groups under hydrogen abstraction conditions to bind to preformed polymer to a substrate in the presence of a free-radical catalyst which removes leaving groups from the carbon chain to form the covalent bonds. See Srinivasan, U.S. Pat. No. 6,074,541. This coating is disclosed for use with a variety of substrates including the inner wall of a conduit or particles for use in a packed bed.
A significant application of ion chromatography is in analyzing water, e.g., surface water and well water. Worldwide, municipal facilities use ion chromatography to qualify water as being appropriate for human consumption. The ionic content of water varies significantly depending on the source, storage and handling conditions. In samples containing high levels of matrix ions such as chloride, sulfate and bicarbonate detecting trace amounts of ions such as bromate or chlorite or perchlorate is challenging.
Methods for ion analysis of water include direct injection and analysis, or pretreating the samples prior to a direct injection analysis. Direct injection is preferred, however, application of this method is limited for some samples with high matrix content due to the limited capacity of the stationary phases currently available. An alternate approach is to pursue pre-concentration of the ions in the sample in conjunction with heart cutting or some means of removing the matrix ions prior to analysis. Heart cutting methods are two-dimensional methods in which the matrix ions are separated or removed in the first dimension, enabling analysis of the ions of interest. Matrix ions are also removed using sample pretreatment with one or more pretreatment cartridges. For example a barium form cation exchange resin based cartridge is used to remove sulfate from the sample matrix. The methods discussed above are multi-step processes with multiple valve configurations, complex plumbing or are labor intensive. Therefore it is desirable to simplify the analysis protocol for samples containing matrix ions. Ion exchange phases having unique enhanced capacity architecture will facilitate analysis.
To counter some of the limitations of existing stationary phases a new phase and method of making this phase was recently introduced (U.S. Pat. No. 7,291,395), and has proven to be a powerful tool for use in chromatography. The stationary phase is formed by building up through condensation polymerization one or more layer on a substrate, each layer having selected structural and functional properties. However, thus far it hasn't been possible to use condensation polymers constructed in this manner for the separation of sulfite and sulfate.
U.S. Pat. No. 5,147,536 describes the use of chromatographic media prepared from ditertiary amines, however, the ditertiary amines used form a polymer with only two carbons between the two quaternary nitrogens in various cyclic structures, and the medium is not used to separate divalent anions. Moreover, the ditertiary amine acts as a cross-linking agent in the polymers compromising the ability to independently control selectivity and capacity during this synthesis. The high cross-linking such materials interferes with rapid mass transport rendering it unsuitable for high-performance analytical applications.
U.S. Pat. No. 4,373,031 describes preparation of anion exchange polymers using ditertiary amines through reaction with vinylbenzylchloride based polymer particles. This approach has the disadvantage set forth above because the ditertiary amine reagent acts as a cross-linking, reagent. Furthermore this patent provides no suggestion of the utility of such materials for improved divalent anion selectivity.
U.S. Pat. No. 5,204,376 describes preparation of anion exchange polymers using ditertiary amines through reaction with chloromethylated polystyrene fibers. Such material suffers from the same disadvantages as described above with the vinylbenzylchloride based polymer particles.
Four patents (U.S. Pat. No. 4,325,940, U.S. Pat. No. 4,089,977, U.S. Pat. No. 4,418,054 and U.S. Pat. No. 4,027,020) describe condensation polymers using 1,3-bis(dimethylamino)-2-propanol but all of these patents describe preparation of soluble polymers and none provide any suggestion of their utility for anion exchange or improving selectivity for divalent anions.
Two patents (U.S. Pat. No. 3,893,982 and U.S. Pat. No. 3,931,444) describe preparation of cured films 1,3-bis(dimethylamino)-2-propanol as the cure catalyst for epoxy containing polymers. In this case, the cured films contain acrylic acid rendering it useless for anion exchange preparations.
High capacity ion exchange phases should provide high resolution of species of interest, particularly dianions, e.g., sulfite and sulfate. Also desirable is an ion exchange stationary phase that provides a basis for separation of two or more dianions from each other, e.g., sulfite, sulfate, carbonate or thiosulfate. These phases should also allow separation and quantitation at trace levels of the separated ions. The present invention provides high capacity stationary phases capable of resolving dianions and methods of making and using them.